Unique dynamic crossover in supercooled x,3-dihydroxypropyl acrylate (x = 1, 2) isomers mixture
The previtreous dynamics in glass forming monomer, glycerol monoacrylate (GMA), using broadband dielectric spectroscopy (BDS) was tested. Measurements revealed the clear dynamic crossover at temperature $T_B = 254$ K and the time scale $τ(T_B) = 5.4$ ns for the primary (structural) relaxation time and no hallmarks for the crossover for the DC electric conductivity $σ_{DC}$. This result was revealed via the derivative-based and distortions-sensitive analysis $dln{H_{a}}/d(1/T)$ vs. $1/T$, where $H_a$ is for the apparent activation energy. Subsequent tests of the fractional Debye-Stokes-Einsten relation $σ_{DC}(τ_α)^S = const$ showed that the crossover is associated with $S = 1$ (for $T>T_B$)->$S = 0.84$ (for $T<T_B$). The crossover is associated with the emergence of the secondary beta relaxation which smoothly develops deeply into the solid amorphous phase below the glass temperature $T_g$.